A wide variety of climbing aids are used to secure individual or groups of climbers to the rock or mountain that they climb. By attaching a rope to one or more climbing aids affixed to the rock and having the rope attached to the climber or climbers, it is possible to limit the distance over which a climber can fall. Since the terrain is frequently difficult to ascend, a fall is not necessarily an unlikely occurrence and the climbing aid provides for a margin of safety which otherwise would not exist.
Climbing aids come in many forms, and most aids may generally be classified as being either active devices or passive devices. Passive devices typically do not include any mechanical or moving parts that assist in attachment of the device to the rock, and instead rely upon friction and gravitational forces to achieve anchoring. Active devices on the other hand generally include some kind of mechanical parts that assist in anchoring the protection on the rock wall.
The simplest form of a passive device is a climbing nut or chock, which typically is simply a piece of metal with a wire or rope loop to attach to it. The piece of metal may be placed snugly into a crack or imperfection in the rock and then attached to the aforementioned rope. Such climbing aids have the significant disadvantage of being unable to adjust to different size cracks and will only work if the rock is of a matching shape for the particular climbing aid.
To improve upon this problem, passive climbing aids of this sort have been geometrically shaped to provide for the possibility of a maximum number of possible fortuitous placements. Some can be placed in three or more possible orientations to increase the chances that a secure (and therefore safe) placement may be found.
In many cases, however, a crack in the rock has nearly smooth sides and there are no features to which such a climbing aid could safely attach. Active climbing aids such as those known as “cams” are useful protection for this type of rock formation, and there are numerous cam devices on the market, and many different mechanisms to operate them. These devices are often referred to as “cams” because they consist of metal pieces in the shape of a logarithmic spiral, “cam members,” free to rotate on one or more axles but directed by springs or other mechanisms so as to expand to fill all the space in a crack. In the event that a force is applied to this type of climbing aid (as in the case of a fall or a load applied to the climbing aid), the physics of the logarithmic spiral provides for a tightening action due to force multiplication on the rock which prevents the device from sliding free of the crack.
To provide some general background information, a climbing cam typically includes one or more pairs of opposed cam members that typically have eccentric outer surfaces. The cam members are pivotally mounted one or more transverse shafts or axles in a way that allows opposed cams to pivot in opposite directions. The cams are spring-loaded and are activated with a trigger. When the trigger is pulled, the cams rotate from their open, extended position toward a closed or compressed position. The compressed cam is then inserted into a crack in a rock, and the trigger is released. When the trigger is released the cam members rotate under the force of the springs back toward their open position until the opposed cams contact the rock.
Assuming that the correct sized cam has been chosen for the crack in question, the cam members engage opposite sides of the crack to provide a frictional engagement with the rock, thereby providing an anchoring point. The cam typically includes a loop or sling of cable attached to it. A carabiner is typically attached to the cable and a loop of webbing is attached to the carabiner. Another carabiner is then connected to the opposite end of the webbing and the rope is passed through the second carabiner. This system allows the rope to move freely through the carabiners without unduly moving the cam and risking it's coming loose. Outwardly directed loads applied to the cam—as when a climber's fall is arrested—causes the cam members jam against the rock as described above.
The variety of sizes that may be accommodated by a climbing aid of the cam type I s often measured in terms of the “expansion range.” The expansion range may be described in various ways, but is typically defined as being numerically equal to the ratio of the largest to the smallest size crack to which the climbing aid may be applied safely. It is well known that for a climbing aid of the cam type with a single axle, the expansion range is limited by interference between the cam members and opposite sides of the crack. This limits the expansion range to about 1.62 for a cam angle of 13.25 degrees. Cams are available in numerous sizes, ranging from very large units having a safe expansion range of up to 4 inches or more, to very small units that have a safe expansion range of less than ½ inch. The safe expansion range of a cam, however, is somewhat less than the actual maximum range of the device.
The particular cam selected by the climber depends on several factors, including for example the topography of the crack into which the cam will be inserted, and the width of the crack. Selection of the correct sized cam and proper placement of the cam is obviously very important since improper sizing and placement can lead to failure of the protection when it is most needed.
Since it is usually the case that the climber does not know exactly what features will appear on the rock, it is necessary to carry several and sometimes many climbing aids of all sorts in order to accommodate all the possibilities which may be required. This increases the weight, bulk, and expense of equipment that is required. There is a need to increase the possibilities for placements of the climbing aids while at the same time decreasing weight. It will be appreciated therefore that it is beneficial to maximize the workable expansion range, as a cam that has a larger expansion range may be used in a wider variety of crack sizes.
U.S. Pat. No. 4,643,377 describes a climbing aid of the cam type in which two parallel axles are employed in order to increase the expansion range. With the appropriate arrangement, it is possible to use slightly larger cam units than on a single axle device and this results in an increase in the overall expansion range to about 1.68. This requires additional weight and mechanical complexity for the device, but these devices have become popular as a consequence of the increase in expansion range.
There is a need therefore for improved climbing cams that have increased working ranges.
Additionally, because a climbing cam is typically not loaded except in a fall or when direct aid from the device is required, due to motion of the climber and the rope, it is possible for the climbing aid to move or rattle around in the crack so as to fall out of the crack, move from the optimal position, or otherwise degrade the placement. This unintentional relative movement between the cam and the rock is often called “walking.” While stiffer springs in the climbing aid may help to alleviate this problem, it would require a large force of perhaps 100 pounds or more to hold the climbing aid in position. At this level, it is not feasible to add springs stiff enough to generate the outward force. There is a need for a mechanism capable of lock the climbing aid in place to prevent it from moving, or to minimize movement of the cam after it is placed.